Darkfall online and EvE Online springs to mind, both good games, but pretty different. (yes, I consider Darkfall very good since I had tons of fun in the 2-3 months I played before having to quit for exams. Most fun I've had in an MMO to date actually, and this is coming from someone who prefers to avoid PvP.) Some posters here are correct though, these games attract a certain kind of gamers, met a good deal of jolly good people in both games though.